The offered Head-UP Display—HUD is intended for flight, navigation, and other parameter presentation on the windshield of aircrafts. Current HUDs utilize wide-angle collimating optical systems and possess great informational resources. HUD forms symbolic images of above-mentioned parameters in its field of view and projecting them to pilot's sight of view into optical “infinity”. These symbolic images are then overlaid on the “real world” picture.
Practically all known HUDs are built the same way and are made up of two rigidly connected parts: an image forming source and collimator optical system. In the patent literature the most frequently described HUDs are the ones where the image forming source is based on a monochromatic projecting CRT (PCRT) with its screen located in the focal plane of the collimator optical system. This high intensity monochromatic PCRT has a relatively high resolution provided by the deflecting and focusing systems, deflection amplifiers and the light amplifier with their inputs connected with symbols generator or integral display system on-board computer according with the signals of which the symbolic data (counters, indices, etc.) is represented on the screen by an electronic beam. To provide high symbol brightness sufficient for the required contrast to be used under the high intensity and ambient lighting conditions, the CRT's electronic beams operated by use of a functional-vector method which provides significantly lower beam velocity during scans than with TV raster representation.
The HUDs described in patents U.S. Pat. No. 4,997,401, U.S. Pat. No. 6,392,812, U.S. Pat. No. 6,567,014 are built by a similar scheme.
The reviewed HUDs based on projecting CRT have significant drawbacks such as the following;
High voltage power supply 15-20 KV is required;
CRT extended electron gun with electrostatic or magnetic focusing is required to provide high brightness and resolution. As a result, the CRT's total length becomes 200-240 mm that makes the rear part of the HUD frame to be extended. As the HUD's rear is positioned behind the instrumental panel, the extremely restricted board space is used inefficiently and instrumental equipment weight is increased.
Limited acceptable beam power density caused by luminofor destruction and focusing system resources excludes the CRT performance improvements. The resolutions of the current CRTs are 10-15 line/mm max for TV-raster mode.
To operate the electron beam by functional-vectorial method powerful DC amplifiers and output transistors are required which need to be cooled by use of bulky and heavy radiators;
Strong power supply is required for deflection amplifiers usually arranged directly inside of HUD, thus increasing size and weight.
To form the image (for example radar or infrared) via a TV-Raster method, the sufficient power supply is required for the deflection amplifiers operation. The specified supplied power is several times more than that of deflection amplifiers supplied power that is required for symbolic images forming by use of functional-vectorial method.
Unstable operating of CRT analog control system caused by outer factors such as temperature, power supply and parameter variations affects the accuracy of aiming data presentation in HUD field of view and therefore it's necessary to introduce an automatic correction schema into the HUD to compensate for the errors caused by above mentioned instability;
To compensate CRT and CRT control system electronic errors which cause angular errors of symbols location the CRT control system is supplemented with an arrangement comprising of adjustable resistors and other electronic components. The process of simultaneous elimination of electronic errors and optical errors caused by optical system distortion is extremely laborious work which is carried out at the production department in the majority of cases.
The HUD disclosed in U.S. Pat. No. 7,482,996 is an example of LCD matrix application as the image forming source. All the main features mentioned in the patent utilize various peculiarities of the polarized light which forms the information picture (“first image”) on the ambient background (“second image”) with natural circular polarization. Actually such approach allows to get a level of enhanced image brightness and contrast that is comparable with similar parameters attained for HUDs based on holographic optical elements and projecting CRT.
At the same time the HUD by U.S. Pat. No. 7,482,996 based on an LCD matrix possesses significant shortcomings caused by limited resolution of the LCD matrix and point structure of image formulation. Therefore the disruptions and “teeth” that are occurring during symbols scans and the symbolic information image is of significantly lower quality than the image formed by the HUD based on CRT, in particular with HUD large fields of view. The offered HUD based on the new conceptual model makes it feasible to eliminate the above-mentioned defect inherent in the display as disclosed in U.S. Pat. No. 7,482,996 and further allows to eliminate or reduce the drawbacks and limitations of the current HUD, based on the CRT, as specified above.